Supercritical injection is used in a diesel engine to prevent ignition delay which is caused by evaporation latent heat generated in liquid phase injection. Furthermore, there is a merit that a mass-based injection rate can be made higher in the supercritical injection than in gas phase injection.
In U.S. Pat. Nos. 7,488,357 B2 and 8,197,558 B2, fuel containing light-oil as a main component and inactive gas such as exhaust gas or liquid CO2 is heated to have a supercritical state, and is supplied to an injector. In this case, the fuel can be injected in the supercritical state, preventing a caulking.
However, in order to make the fuel into the supercritical state from the liquid phase, a very high temperature is required, so large-scale complicated heating system is used to provide the supercritical state before supplying to the injector. Moreover, the system becomes further complicated since a fuel mixture equipment is provided for preventing the caulking in U.S. Pat. Nos. 7,488,357 B2 and 8,197,558 B2.
Moreover, U.S. Pat. Nos. 7,488,357 B2 and 8,197,558 B2 are difficult to be applied to a DME fuel mainly containing dimethyl ether (DME) because a phase change is easily generated in the DME fuel.